Sidewall rubber compositions for tires contain antioxidants for preventing cracks from developing in sidewalls. However, such an antioxidant in a sidewall rubber migrates to the sidewall surface over time, and thus the antioxidant is oxidized at the surface, which causes the sidewall to turn yellow. Moreover, tire component rubbers, which contain many double bonds, have poor weather resistance, and therefore may turn yellow over time. Such sidewall yellowing causes an undesired appearance since tires are originally black due to carbon black. This problem should be overcome to maintain the commercial value of tires.
Patent Literature 1 discloses a method for suppressing migration of an antioxidant to the sidewall surface by using polyethylene glycol having a specific molecular weight. Still, there is a demand for other techniques.